Unlike most of the other things the cats had done during their short trip around the city, their attack on the Blue Lounge pirates actually had justification. The cats had coincidentally encountered the pirates while looking for Toz. At first, they didn't plan on doing anything toward them since they wanted to find Toz and convince him to stay longer in Pirate Haven.
However, that was before they overheard the pirates' plan to sneak attack the Bunglehoppers' base while one of their strongest fighters was away. The Blue Lounge pirates weren't aiming to kill any of the Bunglehoppers. They just wanted to get a feel for the captain's actual strength and possibly destroy some things in the process. With Hayar temporarily away, they were confident in being able to escape and relay the information back to the council that controlled the Blue Lounge League.